1. Field of the Disclosure
The disclosure generally relates to safety devices for gas distribution systems, and specifically relates to slam-shut type safety valves.
2. Related Technology
Gas distribution systems, in particular natural gas distribution systems, typically transport gas from a producer to a consumer along a series of pipes and through a series of valves. Each gas distribution system may include one or more regulator valves that control the pressure of the gas within the distribution system. Normally, the gas is transmitted at a high pressure through the system. However, the pressure of the gas must be reduced prior to final distribution to the consumers. This pressure reduction is typically accomplished at pressure reducing stations within local networks.
Typically, these pressure reducing stations include one or more pressure regulating valves and some sort of safety device to shut off the flow of gas should the pressure regulating valve fail. Most commonly, slam-shut safety valves are used for this purpose when the release of gas to the atmosphere is not desired or allowed. For example, U.S. Pat. No. 4,134,421, which is hereby incorporated by reference herein, discloses a slam-shut safety valve that provides overpressure protection in a pipeline. The slam-shut safety valve is generally disposed upstream of the pressure regulating valve so that the slam-shut valve may prevent gas from reaching the pressure regulating valve in the event of a pressure regulating valve failure. The slam-shut safety valve monitors gas pressure downstream of the pressure regulating valve for maximum and minimum pressure tolerances. If the downstream pressure exceeds either the maximum or minimum tolerance, the slam-shut safety valve closes, cutting off the flow of gas to the pressure regulating valve and preventing an uncontrolled leak of gas due to the pressure regulating valve failure.
Another example of a slam-shut safety valve is disclosed in U.S. Pat. No. 8,225,812, which discloses an over and under pressure protection device. U.S. Pat. No. 8,225,812 is hereby incorporated by reference herein.
Known slam-shut safety valves suffer from several problems. For example, the latching plugs in known slam-shut safety valves were guided by a reset rod, which was susceptible binding if the reset rod bent under high pressure loads from a latching cam. Additionally, known slam-shut safety valves attached the latching plugs to the reset rod with clips, which were subject to failure in high flow velocity valves because the clips could not resist the high kinetic forces generated by the high flow velocity valves. Furthermore, the safety discs of known slam-shut safety devices are easily misaligned when encountering high flow velocities, which resulted in incomplete sealing on the valve port and unreliable shutoffs.